By Alvin Alexander. Last updated: June 4, 2016
Apple Mac OS X FAQ: Where can I find the iLife sound effects?
As of Mac OS X 10.10, the iLife sound effects are under this directory:
/Library/Audio/Apple Loops/Apple/iLife Sound Effects/
Under that directory you’ll find folders named Ambience, Animals, Booms, Foley, Jingles, Stingers, and many more. The sound effects/clips are under those folders.